The present invention relates to a magnetic disk drive. More particularly, the present invention relates to a magnetic disk drive in which a head is retracted if the magnetic disk drive is dropping.
A portable electronic apparatus is subject to shocks due to an accidental drop to the ground, etc. In the case of a portable electronic apparatus provided with a magnetic disk drive, it is a major challenge to protect the portable electronic apparatus from such shocks. In magnetic disk drives, data is written to and read from a rotating magnetic disk by a head which floats above the magnetic disk. Thus, if a portable electronic apparatus provided with a magnetic disk drive is dropped during operation, shocks due to the drop may cause the magnetic disk to be damaged due to collision of the head with the magnetic disk.
According to a known protection mechanism to prevent a magnetic disk from being damaged as mentioned above, if a magnetic disk drive or an electronic apparatus with a magnetic disk drive incorporated detects that the magnetic disk drive or the electronic apparatus is dropping, the head is retracted to a safe place so as to avoid contact with the magnetic disk. Such a protection mechanism is disclosed in, for example, Patent Documents 1 through 3.
Disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2002-100180) is a magnetic disk drive which is provided with a 2-axis acceleration sensor having two detection axes (X and Y axes). This magnetic disk drive detects a dynamic acceleration (shock) and a static acceleration (change in gravity or tilt) from the output signals of the 2-axis acceleration sensor. Further, these detection signals are entered into a CPU in the magnetic disk drive to determine whether or not the magnetic disk drive is dropping. If the magnetic disk drive is dropping, the head is retracted to a ramp position.
Disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2004-146036) is a protection mechanism to protect a magnetic disk drive from landing shock. This protection mechanism recognizes the state of a magnetic disk drive or an electronic apparatus with a magnetic disk drive incorporated, such as a notebook PC, by analyzing the outputs of a 2-axis or 3-axis acceleration sensor mounted outside or inside the magnetic disk drive. Based on the result of analysis, the protection mechanism predicts whether or not the magnetic disk drive will have a shock such as a landing shock. If a shock is predicted to occur, the head is retracted. In addition, the protection mechanism disclosed in Patent Document 2 includes such control as to change the sensitivity for predicting a shock. Namely, if the dynamic situation of the magnetic disk drive is within a certain range for a certain period of time, it is not judged that the magnetic disk is dropping. Further, the protection mechanism disclosed in Patent Document 2 changes the condition for determining to return the retracted magnetic head according to the dynamic situation of the magnetic disk drive before a shock is predicted.
In Patent Document 3 (Japanese Patent Laid-Open No. 2003-263240), an electronic apparatus is disclosed which uses a gravity sensor composed of a mechanical switch which is open in zero gravity state. Based on the output signal of the gravity sensor, the electronic apparatus judges whether it is dropping. If so, the electronic apparatus executes an anti-shock countermeasure such as retracting of the head.
To protect the magnetic disk from a landing shock, it is necessary to promptly retract the head before the landing shock occurs. Thus, to improve the availability of the magnetic disk drive, it is desirable to minimize the time spent to retract the head to the ramp position after it is detected that the magnetic disk drive is dropping. In the above-mentioned Patent Documents 1 through 3, any specific operation to promptly retract the head upon detection of a fall is not disclosed although retraction of the head to the ramp position is disclosed.
Another problem is that giving higher priority to protection from landing shock makes it more likely to judge that the magnetic disk drive is dropping even when it is actually not dropping, that is, increases incorrect detections each of which causes a retraction of the head. Since it is not possible to access the magnetic disk while the head is retracted, increased incorrect detections deteriorate the performance of the magnetic disk drive. Thus, to improve the availability of the magnetic disk drive, it is desirable to suppress incorrect detections. The sensitivity for predicting a shock, namely the condition for judging whether the magnetic disk drive is dropping may be changed according to the dynamic situation of the magnetic disk drive as disclosed in Patent Document 2. In Patent Documents 1 through 3, however, nothing is disclosed as to what action is to be taken concerning the prediction when drop detection is found incorrect.
Further, if the head is retracted to the ramp position due to incorrect drop detection and kept there for a long period of time, the performance of the magnetic disk drive deteriorates since the magnetic disk cannot be accessed. Thus, to improve the availability of the magnetic disk drive, it is desirable to immediately cancel the head retraction and return the head to the magnetic disk if the drop detection is found incorrect. As disclosed in Patent Document 2, the condition for determining to return the head, namely the acceptable value for the dynamic situation of the magnetic disk drive which permits the head to be returned, may be changed adaptively based on the history of the dynamic situation of the magnetic disk drive. However, any of Patent Documents 1 through 3 does not disclose a specific operation to promptly return the head when the drop detection is found incorrect.